This invention generally relates to the delivery to a tumor target site of a therapeutically effective amount of a photosensitizing agent that is activated by a relatively low fluence rate or level of intensity of light administered over a prolonged period of time, and more specifically, to the delivery of a photosensitizing agent that is targeted to bind with cancerous cells at the target site.
One form of energy activated therapy for destroying abnormal or diseased tissue is photodynamic therapy (PDT). PDT is a two-step treatment process, which has received increasing interest as a mode of treatment for a wide variety of different cancers and diseased tissue. The first step in this therapy is carried out by administering a photosensitive compound systemically by ingestion or injection, or topically applying the compound to a specific treatment site on a patient""s body, followed by illumination of the treatment site with light having a wavelength or waveband corresponding to a characteristic absorption waveband of the photosensitizer. The light activates the photosensitizing compound, causing singlet oxygen radicals and other reactive species to be generated, leading to a number of biological effects that destroy the abnormal or diseased tissue, which has absorbed the photosensitizing compound. The depth and volume of the cytotoxic effect on the abnormal tissue, such as a cancerous tumor, depend in part on the depth of the light penetration into the tissue, the photosensitizer concentration and its cellular distribution, and the availability of molecular oxygen, which will depend upon the vasculature system supplying the abnormal tissue or tumor.
Various types of PDT light sources and their methods of use have been described in the prior art literature. However, publications describing appropriate light sources and the effects of transcutaneous light delivery to internal treatment sites within a patient""s body, for PDT purposes, are relatively limited in number. It has generally been accepted that the ability of a light source external to the body to cause clinically useful cytotoxicity during PDT is limited in depth to a range of 1-2 cm or less, depending on the photosensitizer.
Treatment of superficial tumors in this manner has been associated with inadvertent skin damage due to accumulation of the photosensitizer in normal skin tissue, which is a property of all systemically administered photosensitizers in clinical use. For example, clinically useful porphyrins such as PHOTOPHRIN(trademark) (a QLT, Ltd. brand of sodium porfimer) are associated with general dermal photosensitivity lasting up to six weeks. PURLYTIN(trademark), which is a brand of purpurin, and FOSCAN(trademark), which is brand of chlorin, sensitize the skin to light for at least several weeks, so that patients to whom these drugs are administered must avoid exposure to sunlight or other bright light sources during this time to avoid unintended phototoxic effects on the normal dermal tissue. Indeed, efforts have been made to develop photoprotectants to reduce skin photosensitivity (see, for example: Dillon et al., xe2x80x9cPhotochemistry and Photobiology,xe2x80x9d 48(2): 235-238 (1988); and Sigdestad et al., British J. of Cancer, 74:S89-S92, (1996)).
Recently, it has been reported that a relatively intense external laser light source might be employed transcutaneously to cause two-photon absorption by a photosensitizer at a greater depth within a patient""s body, so that it is theoretically possible to cause a very limited volume of cytotoxicity in diseased tissue at greater depths than previously believed possible. However, no clinical studies exist to support this contention. One would expect that the passage of an intense beam of light through the skin would lead to the same risk of phototoxic injury to non-target normal tissues, such as skin and subcutaneous normal tissue, if this light is applied in conjunction with a systemically administered photosensitizer.
For example, one PDT modality discloses the use of an intense laser source to activate a photosensitizer drug within a precisely defined boundary (see: U.S. Pat. No. 5,829,448, Fisher et al., xe2x80x9cMethod for improved selectivity in photo-activation of molecular agentsxe2x80x9d). The two-photon methodology requires a high power, high intensity laser for drug activation using a highly collimated beam, with a high degree of spatial control. For a large tumor, this treatment is not practical, since the beam would have to be swept across the skin surface in some sort of set, repeating pattern, so that the beam encompasses the entire volume of the tumor. Patient or organ movement would be a problem, because the beam could become misaligned. Exposure of normal tissue or skin in the path of the beam and subcutaneous tissue photosensitivity is not addressed in the prior art literature. Any photosensitizer absorbed by normal tissue in the path of the beam will likely be activated and cause unwanted collateral normal tissue damage. Clearly, it would be preferable to employ a technique that minimizes the risk of damage to normal tissue and which does not depend upon a high intensity laser light source to produce two photon effects. Further, it would be preferable to provide a prolonged exposure of an internal treatment site with light at a lower fluence rate or lower intensity, which tends to reduce the risk of harm to non-target tissue or skin and subcutaneous normal tissue and reduces any collateral tissue damage due to phototoxicity.
Other PDT modalities have employed the use of a light source producing a low total fluence delivered over a short time period to avoid harm to skin caused by activation of a photosensitizer and have timed the administration of such drugs to better facilitate destruction of small tumors in animals (see, for example, U.S. Pat. No. 5,705,518, Richter et al.). However, although not taught or suggested by the prior art, it would be preferable to employ a light source that enables a relatively large total fluence PDT, but at a lower intensity so that larger tumor volumes can more readily be treated.
If, as is often the case, a target tumor tissue lies below an intact cutaneous layer of normal tissue, the main drawbacks of all transcutaneous illumination methods, whether they be external laser or external non-laser light sources, are: (1) the risk of damage to non-target tissues, such as the more superficial cutaneous and subcutaneous tissues overlying the target tumor mass; (2) the limited volume of a tumor that can be treated; and (3) the limitation of treatment depth. Damage to normal tissue lying between the light source and the target tissue in a tumor occurs due to the uptake of photosensitizer by the skin and other tissues overlying the tumor mass, and the resulting undesired photoactivation of the photosensitizer absorbed by these tissues. The consequences of inadvertent skin damage caused by transcutaneous light delivery to a subcutaneous tumor may include severe pain, serious infection, and fistula formation. The limited volume of tumor that can be clinically treated and the limitations of the light penetration below the skin surface in turn have led those skilled in this art to conclude that clinical transcutaneous PDT is only suitable for treatment of superficial, thin lesions.
U.S. Pat. No. 5,445,608, Chen et al., discloses the use of implanted light sources for internally administering PDT. Typically, the treatment of any internal cancerous lesions with PDT requires at least a minimally invasive procedure such as an endoscopic technique, for positioning the light source proximate to the tumor, or open surgery to expose the tumor site. There is some risk associated with any internal procedure performed on the body. Clearly, there would be significant advantage to a completely noninvasive form of PDT directed to subcutaneous and deep tumors, which avoids the inadvertent activation of any photosensitizer in skin and intervening tissues. To date, this capability has not been clinically demonstrated nor realized. Only in animal studies utilizing mice or other rodents with very thin cutaneous tissue layers, have very small superficial subcutaneous tumors been treated with transcutaneously transmitted light. These minimal in vivo studies do not provide an enabling disclosure or even suggest how transcutaneous light sources might safely be used to treat large tumors in humans with PDT, however.
Another PDT modality in the prior art teaches the destruction of abnormal cells that are circulating in the blood using light therapy, while leaving the blood vessels intact (see, for example: U.S. Pat. No. 5,736,563, Richter et al.; WO 94/06424, Richter; WO 93/00005, Champan et al.; U.S. Pat. No. 5,484,803, Richter et al., and WO 93/24127, North et al. Instead, it might be preferable to deliberately damage and occlude blood vessels that form the vasculature supplying nutrients and oxygen to a tumor mass, thus rendering a given volume of abnormal tissue in the tumor (not circulating cells) ischemic and anoxic and thus promoting the death of the tumor tissue serviced by these blood vessels.
To facilitate the selective destruction of the blood vessels that service a tumor, it would be desirable to selectively bind a photosensitizing agent to specific target tissue antigens, such as those found on the epithelial cells comprising tumor blood vessels. This targeting scheme should decrease the amount of photosensitizing drug required for effective PDT, which in turn should reduce the total light energy, and the light intensity needed for effective photoactivation of the drug. Even if only a portion of a blood vessel is occluded as a result of the PDT, downstream thrombosis is likely to occur, leading to a much greater volume of tumor necrosis compared to a direct cytotoxic method of destroying the tumor cells, in which the photosensitizer drug must be delivered to all abnormal cells that are to be destroyed. One method of ensuring highly specific uptake of a photosensitizer by epithelial cells in tumor vessels would be to use the avidin-biotin targeting system. Highly specific binding of a targeted agent such as a PDT drug to tumor blood vessels (but not to the cells in normal blood vessels) is enabled by this two step system. While there are reports in the scientific literature describing the binding between biotin and streptavidin to target tumor cells, there are no reports of using this ligand-receptor binding pair to bind with cells in tumor vessels nor in conjunction with carrying out prolonged PDT light exposure (see, for example: Savitsky et al., SPIE, 3191:343-353, (1997); and Ruebner et al., SPIE, 2625:328-332, (1996)). In a non-PDT modality, the biotin-streptavidin ligand-receptor binding pair has also been reported as useful in binding tumor targeting conjugates with radionuclides (see U.S. Pat. No. 5,630,996, Reno et al.) and with monoclonal antibodies (see Casalini et al.; J. Nuclear Med., 38(9):1378-1381, (1997)) and U.S. Pat. No. 5,482,698, Griffiths).
Other ligand-receptor binding pairs have been used in PDT for targeting tumor antigens, but the prior art fails to teach their use in conjunction with targeting cells in blood vessels or treatment of large, established tumors (see, for example, Mew et al., J. of Immunol., 130(3): 1473-1477, (1983)).
High powered lasers are usually employed as a light source in administering PDT to shorten the time required for the treatment (see W. G. Fisher, et al., Photochemistry and Photobiology, 66(2):141-155, (1997)). However, it would likely be safer to use a low power, non-coherent light source that remains energized for two or more hours to increase the depth of the photoactivation. This approach is contrary to the prior art that recommends PDT be carried out with a brief exposure from a high powered, collimated light source.
Recently, there has been much interest in the use of antiangiogenesis drugs for treating cancerous tumors by minimizing the blood supply that feeds a tumor""s growth. However, targeting of tumor vessels using antiangiogenesis drugs may lead to reduction in size of small tumors and may prevent new tumor growth, but will likely be ineffective in causing reliable regression of large, established tumors in humans. However, by using a combination of antiangiogenesis and a photosensitizer in the targeting conjugate, it is likely that a large volume tumor can be destroyed by administering PDT.
In treating large tumors, a staged procedure may be preferable in order to control tumor swelling and the amount of necrotic tissue produced as the PDT causes destruction of the tumor mass. For example, by activating a photosensitizer bound to tumor vessels in the center of a large tumor and then sequentially expanding the treatment zone outward in a stepwise manner, a large volume tumor can be gradually ablated in a controlled fashion in order to prevent swelling due to edema and inflammation, which is problematic in organs such as the brain.
Delivered in vivo, PDT has been demonstrated to cause vessel thrombosis and vascular constriction, occlusion, and collapse. And though the treatment of very superficial, thin tumors has been reported using transcutaneous light, there are no clinical reports of transcutaneous light activation being used to destroy deeper, thick tumors that are disposed more than 2 cm below the skin surface. Clearly, there is a need for a PDT paradigm that enables large volume tumors that are disposed well below the surface of the skin to be destroyed with transcutaneous light activation.
It is apparent that the usual method of administering PDT to treat bulky tumors, which relies on invasive introduction of optical fibers, is not the best approach. It would be highly advantageous to apply light transcutaneously in a completely noninvasive method to treat such large tumors (as well as small and even microscopic tumors), without risking damage to non-target tissues, such as skin and normal subcutaneous tissue. Instead of the conventional technique, a method of photoactivation and a series of photosensitizer constructs is needed that enable PDT-induced cytotoxicity, on both a macro and microscopic scale, without risk to the cutaneous layer, or any surrounding normal tissues. Also, the therapeutic index should be enhanced if a specific photosensitizer drug targeting scheme is employed.
Citation of the above documents is not intended as an admission that any of the foregoing is pertinent prior art. All statements as to the date or representation as to the contents of these documents is based on the information available to the applicants and does not constitute any admission as to the correctness of the dates or contents of these documents. Further, all documents referred to throughout this specification are hereby incorporated by reference herein, in their entirety.
In accord with the present invention, a method is defined for transcutaneously administering a photodynamic therapy to a target tissue in a mammalian subject. The method includes the step of administering to the subject a therapeutically effective amount of either a photosensitizing agent having a characteristic light absorption waveband, a photosensitizing agent delivery system that delivers the photosensitizing agent, or a prodrug that produces a prodrug product having a characteristic light absorption waveband. The photosensitizing agent, photosensitizing agent delivery system, or prodrug selectively binds to the target tissue. Light having a waveband corresponding at least in part with the characteristic light absorption waveband of said photosensitizing agent or of the prodrug is used for transcutaneously irradiating at least a portion of the mammalian subject. An intensity of the light used for irradiating is substantially less than 500 mw/cm2, and a total fluence of the light is sufficiently high to activate the photosensitizing agent or the prodrug product, as applicable.
Preferably, sufficient time is allowed for any of the photosensitizing agent, the photosensitizing agent delivery system, or the prodrug (depending upon which one of these was administered) that is not bound to the target tissue to clear from non-target tissues of the mammalian subject prior to the step of irradiating with the light.
In one application of the invention, the target tissue is vascular endothelial tissue. In another application, the target tissue is an abnormal vascular wall of a tumor. As further defined, the target tissue is selected from the group consisting of: a vascular endothelial tissue, an abnormal vascular wall of a tumor, a solid tumor, a tumor of a head, a tumor of a neck, a tumor of a gastrointestinal tract, a tumor of a liver, a tumor of a breast, a tumor of a prostate, a tumor of a lung, a nonsolid tumor, malignant cells of one of a hematopoietic tissue and a lymphoid tissue, lesions in a vascular system, a diseased bone marrow, and diseased cells in which the disease is one of an autoimmune and an inflammatory disease. In yet a further application of the present invention, the target tissue is a lesion in a vascular system. It is contemplated that the target tissue is a lesion of a type selected from the group consisting of atherosclerotic lesions, arteriovenous malformations, aneurysms, and venous lesions.
The step of irradiating generally comprises the step of providing a light source that is activated to produce the light. In one preferred embodiment of the invention, the light source is disposed external to an intact skin layer of the mammalian subject during the step of irradiating. In another preferred embodiment, the method includes the step of inserting the light source underneath an intact skin layer, but external to an intact surface of an organ of the mammalian subject, and the organ comprises the target tissue.
Preferably, the photosensitizing agent is conjugated to a ligand. The ligand may be either an antibody or an antibody fragment that is specific in binding with the target tissue. Alternatively, the ligand is a peptide, or a polymer, either of which is specific in binding with the target tissue.
The photosensitizing agent is preferably selected from the group consisting of indocyanine green (ICG), methylene blue, toluidine blue, aminolevulinic acid (ALA), chlorins, phthalocyanines, porphyrins, purpurins, texaphyrins, and other photosensitizer agents that have a characteristic light absorption peak in a range of from about 500 nm to about 1100 nm.
The step of irradiating is preferably carried out for a time interval of from about 30 minutes to about 72 hours, or more preferably, from about 60 minutes to about 48 hours, or most preferably, from about 3 hours to about 24 hours.
In yet another application of the invention, the target tissue is bone marrow, or comprises cells afflicted with either an autoimmune disease or an inflammatory disease.
An additional application of the invention contemplates a method for administering photodynamic therapy to a target composition in a mammalian subject by transillumination. The target composition may include one or more pathogenic agents, including: bacteria, viruses, fungi, protozoa, and toxins as well as tissues infected or infiltrated therewith.
Preferably, the total fluence of the light used for irradiating is between about 30 Joules and about 25,000 Joules, more preferably, between about 100 Joules and about 20,000 Joules, and most preferably, between about 500 Joules and about 10,000 Joules.
Another application of the present invention uses an energy activated compound that has a characteristic energy absorption waveband. The energy activated compound selectively binds to the target tissue. Energy having a waveband corresponding at least in part with the characteristic energy absorption waveband of said energy activated compound is used for transcutaneously irradiating at least a portion of the mammalian subject. Preferably the waveband is in the ultrasonic range of energy. Said compound is activated by said irradiating step, wherein the intensity of said ultrasonic energy is substantially less than that level which would result in damage to normal tissue, but at a sufficiently high total fluence of ultrasonic energy that is absorbed by said compound which in turn destroys the target tissue to which it is bound. Preferably, the total fluence of the ultrasonic energy used for irradiating is between about 5 kHz and more than about 300 MHz, more preferably, between about 10 kHz and more than about 200 MHz, and most preferably, between about 20 kHz and more than about 100 MHz.